1. Field of the Invention
The present invention relates to a photodetector element containing a circuit element and manufacturing method thereof. More specifically, the present invention relates to a photodetector element including a circuit element such as a signal processing circuit, used in an optical pickup, an optical remote controller or the like, and to the manufacturing method thereof.
2. Description of the Related Art
FIG. 13 is a schematic cross section showing a specific structure of a photodetector element including a circuit element in accordance with a first related art example.
Such a photodetector element including a circuit element has been widely used for an optical pickup, an optical remote controller or the like. The photodetector element containing a circuit element includes a bonding pad portion 21, a photodiode portion 22 for detecting the received light, and a signal processing circuit portion 23 for processing the received optical signal. The photodetector element containing a circuit element has a multilayered structure including a P type substrate 1, an N type epitaxial layer 5, an SiO.sub.2 film 7, and a surface protecting insulating film 12 in this order from the bottom of the figure. At prescribed positions of p type substrate 1 and N type epitaxial layer 5, an N type buried diffusion layer 2, a P type buried isolating diffusion layer 3, a P type isolating diffusion layer 4, P type diffusion layer 6 and an N type diffusion layer 8 for forming a circuit are formed. Metal layers (aluminum layers, also referred to as metal interconnection portions) 9b to 9f extending at prescribed positions of SiO.sub.2 film 7 are electrically connected to P type diffusion layer 6 or N type diffusion layer 8 mentioned above, and used for providing electrical interconnection on SiO.sub.2 film 7. The surface of the photodetector element containing a circuit element including these metal layers 9b to 9f is covered by a surface protecting insulating film 12, so that direct exposure of metal layers 9b to 9f to the ambient air is prevented.
Further, a metal layer 9a is provided at bonding pad portion 21. At that portion of metal layer 9a which is in the bonding pad portion 21, the surface protecting insulating film 12 is not formed. Therefore, at metal layer 9a in bonding pad portion 21, electrical connection with the outside can be provided.
Such a photodetector element containing a circuit element is encapsulated in a transparent resin mold package, and used as an electronic component.
FIG. 14 is a schematic cross section showing a structure of a photodetector element including a circuit element in accordance with a second related art example.
In the photodetector element containing a circuit element in accordance with the first related art example, it is possible that optical carriers are generated in the silicon substrate because of light incident on the signal processing circuit portion 23, and that a parasitic current is caused by the generated optical carriers, resulting in malfunction of the circuit.
In the photodetector element containing a circuit element in accordance with the second related art example, in order to prevent this malfunction, an interlayer insulating film 10 is formed on the first metal layers 9a to 9f and on SiO.sub.2 film 7, and a second metal layer 11 is formed at the portion of signal processing circuit 23 on interlayer insulating film 10. Protecting film 12 is formed on the second metal layer 11.
More specifically, in the photodetector element containing a circuit element in accordance with the second related art example, a two-layered interconnection structure comprised of the first metal layers 9d to 9f and the second metal layer 11 is used. Since the signal processing circuit 23 is covered with the second metal layer 11, light does not enter the signal processing circuit portion. Therefore, malfunction of the circuit caused by optical carriers can be prevented.
FIG. 15 is a schematic cross section showing a structure of a photodetector element containing a circuit element in accordance with a third related art example. In this example, the second metal layer 11 is used as an interconnection for the signal processing circuit.
FIG. 16 is a schematic cross section showing a structure of a photodetector element containing a circuit element in accordance with a fourth related art example. In this example, a surface anti-reflection film 17 of Si.sub.3 N.sub.4 is formed at photodiode portion 22, which is the photodetector element.
In the above described embodiments, same reference characters denote the same or corresponding portions.
However, the above described photodetector elements containing circuit elements have the following disadvantages.
The photodetector element containing a circuit element in accordance with the first related art example is encapsulated in a transparent resin mold package. However, the transparent resin mold package is not humidity proof. Though the metal interconnections 9b to 9f of aluminum are covered with a protecting film 12, protecting film 12 formed of SiO.sub.2 or polyimide resin has poor resistance to humidity. Therefore, there have been cases where aluminum constituting metal interconnection portions 9b to 9f are corroded by water permeated through the protecting film. Further, metal portion 9a at bonding pad portion 21 is not covered with the protecting film 12, and therefore corrosion is more likely.
In order to solve this problem, a possible solution is to use Si.sub.3 N.sub.4 which is highly resistant to humidity for protecting film 12. In that case, corrosion of metal interconnection portions 9b to 9f can be prevented. However, bonding pad portion 21 is not covered with the protecting film 12, and hence corrosion could not be avoided.
Further, the process for manufacturing the photodetector element containing a circuit element in accordance with the second and third related art examples requires, in addition to the steps for manufacturing the photodetector element containing a circuit element in accordance with the first related art example, (1) the step of depositing interlayer insulating film 10, (2) the step of opening a through hole portion in interlayer insulating film 10, (3) the step of depositing a second metal layer 11, and (4) the step of patterning the second metal layer 11. Increase of the steps (1) to (4) cause increased time necessary for manufacturing the photodetector element containing a circuit element and hence increased manufacturing cost.
Further, in the field of optical pickup and the like, recently, a structure has been proposed in which a light emitting element such as a laser diode chip is directly die-bonded onto the photodetector element containing a circuit element, in order to reduce the size of the device. However, in the structures of the related art examples, there was not a solder material used for direct die-bonding of the laser diode chip, and hence the laser diode chip could not be directly die-bonded.
Further, in the fourth related art example shown in FIG. 16, a anti-reflection film of Si.sub.3 N.sub.4 is formed on the photodiode, which is the photodetector element, in order to improve optical sensitivity of the photodetector element containing a circuit element. When the protecting film 12 is formed by Si.sub.3 N.sub.4 in order to improve humidity resistance in such a structure, the following problem arises.
Referring to FIG. 16, SiO.sub.2 film 7 at photodiode portion 22 which is the photodetector element has a hole, and a anti-reflection film 17 of Si.sub.3 N.sub.4 is formed. In this structure, when Si.sub.3 N.sub.4 is used as surface protecting film 12 with the surface protecting film 12 being stacked on anti-reflection film 17 on photodiode portion 22, surface reflectance varies as the thickness of anti-reflection film (corresponding to the total of the thicknesses of Si.sub.3 N.sub.4 films 12 and 17) vary widely. Therefore, it becomes necessary to remove the surface protecting film 12 at the photodiode portion. However, at the time of etching the surface protecting film 12, Si.sub.3 N.sub.4 film 17 is also etched simultaneously. Therefore, variation in the film thickness of the anti-reflection film is unavoidable.
In order to prevent the variation in film thickness, it is possible to perform the following process steps. First, referring to FIG. 17, when metal interconnection is formed at the signal processing circuit portion 23, a metal pattern 9 is left also on photodiode portion 22. Thereafter, referring to FIG. 18, Si.sub.3 N.sub.4 film 10 which will be the interlayer insulating film is deposited, and a through hole is opened. Thereafter, the second interconnection layer of the signal processing circuit portion and a metal layer 11 which serves to intercept light are deposited, and patterned by common photolithography. Thereafter, surface protecting film 12 of Si.sub.3 N.sub.4 is deposited, and photodiode portion 22 and bonding pad portion 21 are opened. At this time, since photodiode portion is protected by metal patterns 9 and 11, anti-reflection film 15 is not etched.
Thereafter, common photolithography is performed so that metal layers 9 and 11 on the photodiode are removed and the structure shown in FIG. 16 results.
Through the above described manufacturing steps, a photodetector element containing a circuit element which is humidity proof and in which variation in the thickness of reflection protecting film is suppressed, can be provided.
However, according to this process, it is necessary to add the step of photolithography to remove the metal layers on the photodiode, which increases cost. Further, the aluminum film is exposed at the bonding pad portion 21 in this structure, and hence at this portion, resistance to humidity is not sufficient.
In the structure shown in FIG. 16, if a material such as PSG (Phospho Silicate Glass) film or a polyimide film which allows selective etching with Si.sub.3 N.sub.4 is used as surface protecting film 12, the additional step of photolithography becomes unnecessary. At this time, the metal pattern on the photodiode may be removed simultaneously with the patterning of the second interconnection layer. Therefore, an additional step is not necessary at all with respect to the structure of FIG. 14.
However, in such approach, PSG film or polyimide film does not have sufficient humidity resistance, and hence photodetector element containing a circuit element having superior resistance to humidity cannot be provided. In other words, a photodetector element containing a circuit element having superior humidity resistance as well as stable optical sensitivity could not be provided by any of the above described techniques.